1. Field of the Invention
The present invention relates generally to a control system for an internal combustion engine. More particularly, the present invention relates to a method and device for controlling a purge solenoid for a control system of an internal combustion engine.
2. Background Information
Under normal operating conditions, fuel evaporates from inside an automotive vehicle's fuel tank. These vapors are temporarily stored inside of a vapor storage canister generally known as a purge canister or vapor canister. A typical purge canister contains a quantity of activated charcoal as the preferred medium for storing the fuel vapors. Because the purge canister's storage capacity is limited by the charcoal becoming saturated with absorbed fuel vapor, it is necessary to periodically purge the canister with fresh air to remove the fuel vapor.
Typically, a control system is used to purge the canister. The control system includes a purge solenoid which is turned ON and OFF to control fuel vapor purged from the purge canister to the internal combustion engine. An example of such a control system is disclosed in U.S. Pat. No. 5,263,460, issued to Baxter et al. and in U.S. Pat. No. 4,821,701, issued to Nankee II et al., the disclosures of which are hereby incorporated by reference. Although the above systems have worked well for their intended purposes, there exists a need to better control and vary the amount of purge flow from the purge canister to the internal combustion engine.
It is therefore one object of the present invention to provide a method of controlling purge flow to an internal combustion engine.
It is another object of the present invention to provide a method of varying the amount of purge flow to the internal combustion engine.
It is yet another object of the present invention to utilize a linear purge control solenoid, also known as a proportional purge solenoid (PPS), to control fuel vapor purged from the purge canister.
It is a further object of the present invention to provide a pulse width modulated (PWM) driver to allow for accurate purge flow scheduling.
To achieve the foregoing objects, the present invention is a method of controlling a proportional purge solenoid for a purge control system of an internal combustion engine. The present method obtains a desired target current based upon the engine vacuum and the desired purge flow. PID feedback is incorporated in the desired target current flow through the modifying of the delivered duty cycle to the proportional purge solenoid driver.
One advantage of the present invention is that the method will allow for more accurate control of a linear purge control solenoid. The flow through a linear purge control solenoid is best controlled using a current feedback method since the coil resistance varies with changes in operating temperature.
Additional objects, features and advantages of the invention will become more fully apparent to persons skilled in the art from a consideration of the Detailed Description of the Preferred Embodiment and the appended claims, both when taken in conjunction with the accompanying drawings.